The present invention relates to an a method for cleaning a solid surface, and particularly more to a method for cleaning a part such as a metal workpiece, a printed circuit board or the like, which has a surface having a complicated shape.
In the prior art, a cleaning apparatus and method using dry ice particles is disclosed in Japanese Patent Laid-Open No. 63-266836, and an ice fine particle generating apparatus using ice fine particles is disclosed in Japanese Patent Laid-Open No. 63-283133. In these methods and apparatuses, fine particles of dry ice or ice are blown out of a nozzle and sprayed on a substance to be cleaned for removing contaminants from the surfaces of the substance.
In addition, in other prior art, chlorine-type organic solvents such as trichloroethylene and the like and 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113 in abbreviation) are generally used for cleaning the oils, greases and waxes adhering to metal workpieces, printed circuit boards and the like.
In the above-described prior art, the former method using fine particles is effective to clean a flat board such as a glass board, a Si wafer or the like. However, this method cannot uniformly clean the whole surface print circuit board on which many electronic parts are mounted, a part having a convex and concave surface or a complicated structure with holes because the motion of the dry ice used for cleaning in a constant direction causes a shadow portion on which the fine particles cannot be sprayed.
The prior art method using a chlorine-type organic solvent such as trichloroethylene or the like has a danger of contaminating underground water, and, since CFC-113 depletes the stratospheric ozone, the use thereof is severely restricted.